In recent years, navigation systems that enable a driver to easily reach a desired destination by providing vehicle travel guidance are often provided in vehicles. The term navigation system here refers to a system configured to detect the current position of a host vehicle using a GPS receiver or the like, obtain map data corresponding to the current position through a network or a storage medium such as a DVD-ROM or a HDD or the like, and display that map data on a liquid-crystal display (LCD). In addition, this navigation system includes a route searching function that searches the optimum route from a point of departure to a destination when a desired destination is input. The navigation system then reliably guides a user to the desired destination by displaying a guide route set based on the search results by the route searching function on a display screen, and performing guidance using voice or the display screen when the host vehicle approaches a branch point for which guidance, such as for a left or right turn, is to be performed (hereinafter simply referred to as a “guide branch point”). Also in recent years, some mobile phones, Personal Digital Assistants (PDA), and personal computers and the like also have a function similar to that of the navigation system described above. Moreover, this kind of guidance can also be performed for pedestrians and bicyclists, as well as vehicles.
Here, when guidance for a left or right turn or the like is performed at a guide branch point, the guide branch point must be accurately identified by the user. Therefore, the timing at which guidance starts and the timing at which guidance ends according to a guidance prompt must each be set appropriately. For example, when providing the guidance “turn left at the second light” using a traffic light, guidance preferably starts after the traffic light that is two traffic-light branch points before the guide branch point disappears from the view of the user, and guidance preferably ends while the traffic light that is one traffic-light branch point before the guide branch point is still viewable by the user. Therefore, Japanese Patent Application Publication No. 2002-156242 (JP-A-2002-156242), for example, describes technology that, when performing guide branch point guidance with voice guidance in which the number of traffic lights is used, performs voice guidance using the number of traffic lights when the output of voice guidance ends before passing through the traffic light that is one traffic-light branch point before the guide branch point, and does not perform voice guidance when the output of voice guidance will not end before passing through the traffic light that is one traffic-light branch point before the guide branch point.